CA2640777A1 - Metal carbonitride layer and method for the production of a metal carbonitride layer - Google Patents

Abstract

The invention relates to a method for coating a tool or tool part, especially a cutting element such as a cutting plate, in which a basic member is supplied and one or several layers are applied to the same, at least one layer being made of a metal carbonitride of one or several of the metals comprising titanium, zirconium, hafnium, vanadium, niobium, tantalum, and/or chromium and being deposited by means of a gas containing methane, nitrogen, and one or several metal compounds. In order to obtain a metal carbonitride layer on which additional layers that have great adhesive strength can be deposited and which is provided with great resistance to wear, the deposition process of the metal carbonitride layer is started at a temperature of the basic member of 850 to 950 ~C, whereupon the temperature of the basic member is increased by at least 40 ~C and the deposition process is continued at least in part at the increased temperature. The invention further relates to a metal carbonitride layer that is applied to an object, as well as a tool or tool part, particularly a cutting element such as a cutting plate, encompassing a basic member with one or several layers that are applied thereto, at least one layer representing a metal carbonitride layer which has a nanocomposite structure.

Description

P33589.S01 Metal Carbonitride Layer and Method for the Production of a Metal Carbonitride Layer The invention relates to a method for coating a tool or tool part, in particular a cutting element such as an insert, in which a base structure is provided and one or more layers are applied thereto, at least one layer being formed of a metal carbonitride of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium and being deposited by means of a gas containing methane, nitrogen and one or more metal compounds.

Furthermore, the invention relates to a coating applied to an object with at least one metal carbonitride layer of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium, e.g., a titanium carbonitride layer.

Furthermore, the invention relates to a tool or tool part, in particular a cutting element such as an insert, comprising a base structure with one or more layers applied thereto, at least one layer being a metal carbonitride layer.

Abrasively highly stressed tools, e.g., cutting, stamping or forming tools, are usually coated in order to counteract wear of the tools during use. Multilayer coatings with an outermost workpiece-side working layer and several layers or plies lying underneath are also thereby often used. Although multilayer coatings are more complex to produce than single-layer coatings, with the same thickness they are less brittle and connected with greater flexibility when it is a matter of designing a coating in the best possible manner with respect to anticipated stresses.

From the prior art multilayer coatings are known for inserts of lathe tools, which coatings have a titanium nitride layer or aluminum oxide layer as the outermost layer on the workpiece side during use, which layer is deposited directly or indirectly on a metal carbonitride layer such as a titanium carbonitride layer. The aluminum oxide layer, for example, is chemically inert and heat-resistant and thus protects the layers lying underneath. The supporting titanium carbonitride layer is characterized by great hardness and is intended to contribute to a wear resistance of the coating or of the tool. Further layers can be provided between the connecting layer of titanium carbonitride and the base structure of the insert of hard metal, in particular layers that adhere well to the base structure, thus rendering possible a strong adhesive connection of the coating.

IP33589 00321484.DOC) 1 P33589.S01 It must be taken into account with multilayer coatings that a great hardness of individual layers alone is not yet sufficient for a long operational life or service life. Even an extremely hard layer can no longer be useful if it detaches from the base structure or a layer lying underneath, which can occur in particular with inserts, which are subjected not only to high mechanical stresses but also to high temperatures and/or temperature changes.

Particularly high demands are made on connecting layers or intermediate layers of metal carbonitride (MeC,,Ny) in this context, since their very function is to give the coating wear resistance and to bear a protecting working layer for a long time.

In particular layers of titanium carbonitride are particularly frequently used connecting layers in multilayer coatings or layer systems. The reason for this is that with known titanium carbonitride layers, carbon can be replaced consistently by nitrogen (or vice versa), whereby the properties of these layers can also be variably adjusted via the composition. Finally, layers of this type have properties that lie or can be set between those of titanium carbide and titanium nitride.

A production of titanium carbonitride layers can be carried out by means of CVD
methods (chemical vapor deposition), as was the practice for many years, the layers being deposited from a gas mixture containing methane, nitrogen, titanium tetrachloride and hydrogen as carrier gas at substrate temperatures from 950 to 1100 C. The titanium carbonitride layers thus obtained are composed of globular grain and form a dense layer.
In connection with the deposition of this so-called high-temperature titanium carbonitride on hard metal substrates, an undesirable decarburization of the substrate is often observed, even when a connecting layer, e.g., an 0.5 gm thick layer of titanium nitride, is provided between the hard metal and the titanium carbonitride layer. In order to curb this decarburization, there has recently been a switch to using gases containing titanium tetrachloride and acetonitrile for the deposition of titanium carbonitride, whereby a deposition temperature can be reduced to lower temperatures of 750 to 900 C.
Titanium carbonitride produced in this manner is known as medium-temperature titanium carbonitride and has a columnar structure of rod-shaped crystallites, the thickness of which is more than 750 A or 75 nanometers.

{ P33589 00321484.DOC) 2 P33589.S01 As mentioned, known high-temperature or medium-temperature titanium carbonitride layers are used primarily as connecting layers on which further layers are or will be deposited. However, it has been shown that an adhesive strength of titanium nitride layers or other types of working layers can be insufficient on conventional titanium carbonitride layers as on other metal carbonitride layers, too, so that an operational life of the tool can be limited by a detaching of a working layer that is wear resistant per se.

In addition, known titanium carbonitride layers and metal carbonitride layers in general are also used as outermost layer arranged on the workpiece side, thus as a working layer.
However, in practice they can thereby be used only in a very restricted manner: with layers of this type, when used as a working layer, sticking and thus, despite great hardness, a comparatively short service life is to be anticipated.

Starting from this basis, the object of the invention is to disclose a method of the type mentioned at the outset, with which a metal carbonitride layer can be applied, on which, on the one hand, further layers with high adhesive strength can be deposited and which, on the other hand, is highly wear-resistant, so that the coated tool or tool part optionally can be used immediately.

The object of the invention is also to disclose a coating of the type mentioned at the outset applied to an object, which coating has at least one metal carbonitride layer, e.g., titanium carbonitride layer, on which, on the one hand, further layers with high adhesive strength are deposited and which, on the other hand, is highly wear-resistant such that the coated tool or tool part optionally can be used immediately.

Furthermore, an object of the invention is to create a tool or tool part of the type mentioned at the outset in which the metal carbonitride layer is highly wear-resistant and ensures a high adhesive strength of a layer optionally deposited thereon.

The method-related object of the invention is attained by a method according to claim 1.
Favorable variants of a method according to the invention are the subject matter of claims 2 through 7.

The advantages obtained with the invention are particularly that a metal carbonitride layer, e.g., a titanium carbonitride layer, is generated with a microscopic structure that is S P33589 0032 ] 484.DOC ) 3 P33589.SO1 excellently suitable for the deposition of further layers with strong adhesion. In terms of crystal chemistry, the crystals respectively have an inhomogeneous element distribution over the cross section. The layers, e.g., of titanium nitride, aluminum oxide or diamond, subsequently applied adhere to such layers in a much improved manner and separation does not occur even under the harshest operating conditions or occurs only with much reduced intensity.

It was also unexpectedly determined that a layer deposited according to the invention also exhibits excellent wear behavior compared to conventional metal carbonitride layers and therefore can also be used advantageously as a working layer. This observation is all the more surprising if one considers that especially a titanium carbonitride layer deposited according to the invention has a lower hardness (or microhardness) with the same chemical composition than a titanium carbonitride layer with granular structure produced in a conventional way.

In carrying out the method according to the invention, it is advantageous if the temperature of the base structure is increased with progressive deposition. An uninterrupted growth of the metal carbonitride layer is thus given, which proves to be favorable with respect to a layer structure free from defects as far as possible.

In order to avoid a metal nitride layer beginning to form in some areas after initial formation of metal nitride nuclei, it is expedient for the temperature of the base structure to be brought to an increased temperature within 350 minutes, in particular 120 minutes, after the start of deposition.

It is advantageous for a high stressability of the deposited metal carbonitride layer if the deposition is continued for at least 60 minutes after increased temperature has been reached, so that a minimum layer thickness of at least 0.5 m is set.

An increased temperature is preferably 1010 to 1040 C. In this temperature range the individual crystals grow quickly and with few defects, so that a rapid growth of a highly stressable layer results.

Particularly excellent coatings with respect to the wearing qualities of the tool or tool part can be obtained if a titanium carbonitride layer is formed and deposited by means of a gas 1P33589 00321484.DOC 1 4 P33589.S01 containing methane, nitrogen and titanium tetrachloride. In this connection, it has proven of value for the gas to contain methane, nitrogen and hydrogen in a molar ratio of 1:(8 to ll) :(15 to 25) and the gas to contain I to 8 % by volume titanium tetrachloride.
Undesirable proportions of granular titanium carbonitride can thus he substantially reduced or avoided and the advantages achieved according to the invention increased still further. A composition of the layer in this case is TiCXNy with x being 0.15 to 0.25 and y being 0.85 to 0.75.

A pressure of the reactive gas is not critical per se and can be varied within broad limits.
The titanium carbonitride layer is preferably deposited at a pressure of 100 to 800 millibar, preferably 200 to 400 millibar.

The further objective of the invention of disclosing a coating, applied to an object, with at least one metal carbonitride layer of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium, e.g., a titanium carbonitride layer, which is highly wear-resistant and on which optionally further layers with high adhesive strength can be deposited, is attained if the metal carbonitride layer has a nanocomposite structure that is formed from crystals with inhomogeneous element distribution.

The advantages achieved with the invention are in particular that a metal carbonitride layer with nanocomposite structure, e.g., a titanium carbonitride layer of this type, with a microscopic structure is available, which is excellently suitable for the deposition of further layers with strong adhesion.

One skilled in the art understands a nanocomposite structure of the layer to mean an embodiment with several phases that have a measurement in the nano range.
Surprisingly, tests have shown that there is essentially no decarburization at all in the near-surface area of the substrate and that no indiffusion of the binder phase in the metal carbonitride layer occurred, either.

The composite structure with a plurality of individual crystals in the nano size range also yields a substantially enlarged grain boundary area, whereby the toughness of the layer is increased.

(P33589 0032I484.D C j 5 P33589.S01 Since the metal carbonitride crystals have grown in the nano size range during coating, the surface is fissured and during the deposition of a further layer offers structurally quasi a plurality of small individual points or spikes, which are advantageous for a multiple anchoring. The layers, e.g., of titanium nitride, aluminum oxide or diamond subsequently applied therefore adhere in a much improved manner and a separation does not occur even under the harshest operating conditions or occurs only with much reduced intensity.
It was also unexpectedly determined that a layer deposited according to the invention also exhibits an excellent wear behavior compared to conventional metal carbonitride layers and can therefore also be used advantageously as a working layer. This observation is all the more surprising if one considers that especially a titanium carbonitride layer deposited according to the invention has a lower hardness (or microhardness) with the same chemical composition than a titanium carbonitride layer with granular structure produced in a conventional way.

If the crystals have different contents of carbon and of nitrogen in their chemical composition in the center and in the marginal area according to a preferred embodiment, a layer can be produced with particularly good wear properties.

The toughness and adhesive strength of the metal carbonitride layer can be further increased if at least two types of crystals with different geometric shape form the layer.
The strength and toughness of the metal carbonitride layer itself as well as a connection with a grown layer, e.g., a titanium nitride or aluminum oxide layer, can be increased if the layer is formed from at least one type with star-shaped acicular structure and at least one type with lamellar structure.

In one embodiment variant the layer of metal carbonitride can be doped with boron, silicon, zircon, hafnium, vanadium or rare earths in order, for example, to increase a hot hardness of the layer. Doped in this context means individual contents up to 0.01 % by weight, based on the total weight of the layer.

It is particularly advantageous if rod-shaped crystallites in the arithmetic average have a thickness of less than 65 nanometers, preferably less than 45 nanometers. The finer the crystallites, the better the action of an anchoring effect in the deposition of a layer on the {P33589 00321484.DOC) 6 P33589.S01 metal carbonitride layer according to the invention and the greater the adhesion of the layer additionally deposited.

According to a preferred embodiment of the invention, the mean size of the crystals increases towards the outside, i.e., the workpiece side. In this manner, on the one hand, a high anchoring quality of the metal carbonitride layer on an area lying beneath, for example, on a hard metal cutting insert of a tool, is achieved, on the other hand, even without further layers a long working life of the part can be advantageously achieved.
According to the invention a metal carbonitride layer of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium, for example, a titanium carbonitride layer, which is highly wear-resistant and on which optionally further layers with high adhesive strength are deposited, has a composition MeC,Ny with x being 0.1 to less than 0.3 and y being 0.9 to more than 0.7.

Since titanium nitride has a much lower hardness compared to titanium carbide, it was surprising to one skilled in the art that a titanium carbonitride according to the invention with a carbon content of less than 0.3 on average forms a highly wear-resistant layer and a coated tool can be used directly in a practical manner, e.g., in a cutting of metal material, with a high service life.

It is unexpected particularly for a titanium carbonitride layer that a microhardness of a layer according to the invention is only approx. 2000 H,, and is thus considerably lower than those conventional titanium carbonitride layers which (with increasing carbon content) can be 2300 to 3400 H. It is also surprising in this context that despite marked carbon content in the layer sticking is greatly reduced, which has a positive effect on the wear behavior.

The wearing quality of the coating can thereby have a maximum level when the values are x= 0.15 to 0.20 and y= 0.85 to 0.80.

A metal carbonitride layer according to the invention is optically characterized in that the color of the layer is a yellowish red shade with a light/dark structure, in particular with the like vein structure, which is also discernible at 500 - 1000 x magnification in the micrograph in the optical microscope.

( P33589 00321484DOC 1 7 P33589.S01 The further object of the invention to create a tool or tool part of the type mentioned at the outset with applied coating, with which the metal carbonitride layer is very strongly anchored and wear-resistant and ensures a high adhesive strength of a layer optionally deposited thereon, is achieved in that the metal carbonitride layer is a coating applied according to one of claims 8 through 17. Advantageously, the carbonitride layer is formed on the outside, i.e., on the workpiece side, in a star-shaped acicular manner and bears a top layer, formed as an oxide layer, preferably an aluminum oxide layer (A1203) or a carbon layer, in particular a diamond layer.

Advantages of a too] or tool part according to the invention are in particular that the metal carbonitride layer provided on the one hand is more wear-resistant than conventional metal carbonitride layers and on the other hand, when another layer is deposited on the metal carbonitride layer, links and anchors it strongly, which likewise proves advantageous for an operational life of the tool or tool part.

Although different layers can be applied, e.g., as working layers, to the metal carbonitride layer with a tool according to the invention, a particularly strong adhesion is observed when a layer of titanium aluminum nitride is applied. Layers of aluminum oxide, A1203, or diamond can also be applied with particularly good adhesive strength to a metal carbonitride layer according to the invention, in particular a titanium carbonitride layer.
Further advantages and favorable effects of a tool according to the invention result from the context of the specification and the following exemplary embodiments, based on which the invention is described in still more detail.

They show:

Fig. 1: An SEM photo of the surface of a Ti(CN) layer according to the invention (SEM -Scanning Electron Microscopy);

Fig. 2: Image of a TEM test (TEM - Transmission Electron Microscopy);

Fig. 3: A micrograph of the transition of a coating (microsection ground at an angle of 15 );

Fig. 4: A representation of a wear land width vb determined experimentally versus a number of cuts for indexable inserts with different coatings;

I P33589 00321484.DOC) 8 P33589.S01 Fig. 5: A diagrammatic representation of the temperature variation during a coating Fig. 1 shows an SEM image of the surface of a titanium carbonitride layer according to the invention. The layer has grown on the substrate in a composite structure with star-shaped needles and thicker lamina embedded therein. The lamina have a largest longitudinal extension of approx. 1 pm, are flat and have a width on average of approx.
0.7 m, however, the star-shaped needles are embodied with a much smaller thickness.
The lamellar and acicular crystals have an inhomogeneous element distribution and also have different average composition in comparison.

The formation of a surface of a metal carbonitride layer structured in this manner provides the best conditions for a high adhesive strength of an applied subsequent layer.
Tests by means of x-ray diffraction using CuK radiation were used to identify the crystalline phases in the layer. Evaluations of the XRD measurements yielded a C/N ratio in the range of C/N = 0.14 to 0.19/0.86 to 0.81 with a layer according to the invention.
An average grain size determined according to Scherrer yielded values of 26 and 17 nm.
The layer thus has a nanostructure.

Dark areas labeled 1 and light areas with reference number 2 are discernible from Fig. 2 of a TEM image. In the tests of this sample in comparison the dark areas are richer in carbon and the lighter areas are richer in nitrogen. A demixing with respect to the composition of the grains can thus be clearly seen, which reveals a specific core/sheath structure of the grains.

The free surface of a titanium carbonitride layer according to the invention is embodied in a markedly fissured and acicular manner at the transition to a working layer subsequently deposited (Fig. 3). This surface structure promotes a strongly adhesive deposition of subsequent layers, since an intimate permeation of the layers occurs in the border area. A deviation of individual crystals from an exact 90 position in the surface area is thereby definitely desirable, since corresponding irregularities lead to a better interlacing of the layers with one another.

(P33589 00321484.DOC ) 9 P33589.S01 Fig. 4 shows data on wearing tests with indexable inserts that had multilayer CVD
coatings with a structure according to Table 1. The hard metal substrate and the insert geometry were identical for all indexable inserts.

Table 1: Structure and layer thickness of multilayer coatings for inserts A
through C
Layer Layer thickness [ m]

A B C
TiN 0.5 0.5 0.5 MT-TiCN* 10.0 3.0 3.0 E-TiCN* * 4.0 7.0 A1203 3.0 3.0 3.0 TiN 0.5 0.5 0.5 Total 14.0 11.0 14.0 * ... Medium-temperature titanium carbonitride ** ... Titanium carbonitride deposited according to the invention The indexable inserts were tested under the following test conditions with a rotary machining of the material.

Machined steel: 34 CrNiMo 6, 261 HB
Cutting speed vc: 280 m/min Cutting depth aP: 1.50 mm Feed f: 0.28 mm/U

Stepped cut with emulsion, each cut 30 seconds As can be seen from Fig. 4, under the same operating conditions indexable inserts B and C have a much smaller wear land width compared to indexable insert A with the same connecting layer to the hard metal (0.5 pm TiN) and the same outer layer (0.5 pm TiN).
After 20 cuts a wear land width for indexable insert A is 0.50 m, whereas for indexable insert B 0.32 pm and for indexable insert C 0.14 m were determined. Compared to the (P33589 00321484.DOC ) 10 P33589.S01 layer thicknesses of indexable inserts B and A, it can be established that an increased wear resistance is achieved despite smaller layer thickness. This means advantages in terms of production engineering, since approx. 1 hour per m layer thickness must be allowed with a deposition by means of CVD processes. More wear-resistant coatings can now therefore be produced in a shorter time.

Further tests showed that a titanium carbonitride layer according to the invention can also be used advantageously as an outermost working layer. With otherwise the same layer structure and the same layer thickness, inserts with an outermost layer of titanium carbonitride according to the invention are superior by 1.5-fold or more to inserts with medium-temperature titanium carbonitride as a working layer in terms of service life, even if the microhardness is lower. This effect is attributed to the special structure of titanium carbide layers produced according to the invention.

Fig. 5 shows diagrammatically and by way of example a procedure with a coating according to the invention based on a time-temperature diagram: at a temperature Tl of the base structure or the reaction chamber of approx. 960 C (time "0"), reaction gas containing methane, nitrogen, hydrogen in a ratio of 1:10:20 and 4 % by volume titanium tetrachloride is added, whereby, as is assumed, rod-shaped titanium nitride nuclei are deposited. Subsequently the temperature is consistently increased to 1050 C
within 150 minutes with constant contact with the reaction gas; the temperature increase from 960 to 1050 C however can also be carried out incrementally. Finally, the coating is continued for another 250 minutes at 1050 C and with the same composition of the reaction gas and then ended.

) P33589 00321484.DOC ) 1 1

Claims (19)

1. Method for coating a tool or tool part, in particular a cutting element such as an insert, in which a base structure is provided and one or more layers are applied thereto, at least one layer being formed of a metal carbonitride of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium and being deposited by means of a gas containing methane, nitrogen and one or more metal compounds, characterized in that the deposition of the layer of metal carbonitride is begun at a temperature of the base structure of to 950°C, after which the temperature of the base structure is increased by at least 40°C and the deposition is continued at least for a time at increased temperature.

2. Method according to claim 1, characterized in that the temperature of the base structure is increased with progressive deposition.

3. Method according to claim 1 or 2, characterized in that the temperature of the base structure is brought to an increased temperature within 350 minutes, in particular 120 minutes, after the start of deposition.

4. Method according to one of claims 1 through 3, characterized in that after an increased temperature is reached, the deposition is continued for at least 60 minutes.

5. Method according to one of claims 1 through 4, characterized in that the increased temperature is 1010 to 1040° C.

6. Method according to one of claims 1 through 5, characterized in that a titanium carbonitride layer is formed and deposited by means of a gas containing methane, nitrogen and titanium tetrachloride.

7. Method according to claim 6, characterized in that the gas contains methane, nitrogen and hydrogen in a molar ratio of 1 : 8 to 11 : 15 to 25 and the gas contains 1 to 8 % by volume titanium tetrachloride.

8. Coating applied to an object with at least one metal carbonitride layer of one or more of the metals titanium, zircon, hafnium, vanadium, niobium, tantalum and/or chromium, e.g., a titanium carbonitride layer, characterized in that the metal carbonitride layer has a nanocomposite structure that is formed from crystals with inhomogeneous element distribution.

9. Coating with a metal carbonitride layer according to claim 8, characterized in that the crystals in their chemical composition in the center and in the marginal area have different contents of carbon and of nitrogen.

10. Coating with a metal carbonitride layer according to claim 8 or 9, characterized in that at least two types of crystals with different geometric formation form the layer.

11. Coating with a metal carbonitride layer according to one of claims 8 through 10, characterized in that the layer is formed from at least one type with star-shaped acicular structure and at least one type with lamellar structure.

12. Coating with a metal carbonitride layer according to one of claims 8 through 11, characterized in that the layer is doped with B, Si, zircon, hafnium, vanadium or rare earths.

13. Coating with a metal carbonitride layer according to one of claims 8 through 12, characterized in that the crystals have an average size under 65 nm, preferably under 45 nm.

14. Coating with a metal carbonitride layer according to one of claims 8 through 13, characterized in that the average size of the crystals increases towards the outside, i.e., the workpiece side.

15. Coating with a metal carbonitride layer according to one of claims 8 through 14, characterized in that the layer has a composition MeC x N y, x being 0.1 to less than 0.3 and y being 0.9 to more than 0.7.

16. Coating with a metal carbonitride layer according to claim 15, characterized in that the values are x = 0.15 to 0.20 and y = 0.85 to 0.80.

17. Coating with a metal carbonitride layer according to one of claims 8 through 16, characterized in that the color of the layer is a yellowish-red shade with a light-dark structure, in particular with a vein structure of the like, which is also discernible at 500 - 1000 x magnification in the micrograph in the optical microscope.

18. Tool or tool part, in particular cutting element like an insert, comprising a base structure with one or more layers applied thereto, at least one layer being a metal carbonitride layer, characterized in that a coating one of claims 8 through 17 is applied.

19. Tool or tool part according to claim 18, characterized in that the carbonitride layer is formed on the outside, i.e., on the workpiece side, in a star-shaped acicular manner and bears a top layer, formed as an oxide layer, preferably an aluminum oxide layer (Al2O3) or a carbon layer, in particular a diamond layer.